Nanotechnology, in particular synthesis and use of nanoparticles, is introduced in many fields and features a plurality of possible applications such as chemical or biological detectors, drug delivery systems, new generation of laser, reinforced materials, thermal barriers and ink jet systems as well as textiles.
Most of the known synthetic methods for the production of silver nanoparticles rely on the use of organic solvents, such as acetone, chloroform, DMSO, etc., and toxic reducing agents, such as hydrazine, DMF, sodium borohydride, etc., in addition to separate stabilizing agents. All previous chemicals are toxic and pose potential environmental and biological risks. Besides this, said substances cause high costs and are therefore not favorable for an industrial application.
Vigneshwaran et al., Carbohydrate research, 2006, 341, 2012-2028, relates to the “green” synthesis of stable silver nanoparticles using soluble starch. It is disclosed that the preparation was carried out in an autoclave at 15 psi at 121° C. for 5 minutes. The nanoparticles obtained this way were found to be stable in aqueous solution over a period of 3 months at room temperature. Soluble starch in terms of this disclosure means linear amylose which was obtained from native starch by separation from the insoluble part (branched amylopectin). The disclosed nanoparticle solutions featured a low concentration of only 50 ppm of silver nanoparticles.
US 2010/0172997 A1 relates to gold, silver and copper nanoparticles stabilized in biocompatible aqueous media. It is disclosed that the nanoparticles can be prepared by photo reduction and thermolysis. Biopolymers such as chitosan, PVA, HPC, PEG, algenic acid etc. were used as stabilizing agents.
US 2007/0269880 A1 relates to a stabilizing solution for submicronic particles. In particular, the synthesis of silver and gold nanoparticles using bitter gourd extract is disclosed. The particles prepared this way feature diameters in a range from 20 to 150 nm. Moreover, a broadening in size distribution of the formed particles was observed.
US 2006/0045916 A1 relates to a method for preparing silver nanoparticles by the reduction of silver ions using phosphine amino acids. The particles are stabilized by a starch previously dissolved in water at a temperature of 100° C.
It is an object of the present invention to provide well stabilized, highly concentrated compositions comprising nanoparticles having a narrow size distribution which can be prepared at low costs under ambient conditions.